Volt-ampere-hour meter



1938. w. H. PRATT VOLT-AMPERE-HOUR METER Filed Oct. 7, 1937 Inventor William H. Pratt, Hi2 Attorney Patented Nov. s, 1938 VOLT-AIVIPERE-HOIZR -ME William H. Pratt, Lynn, Mass; assigirior to eral Electric Company, a c orporation of New V 7 York Application October 7; 1937, Srial No- 167,7 53- 5Claims. (Cl.1 71 264);.

Myinvention relates to volt-ampere hour meters and .itsrobject is to provide a relatively inexpensive but reliable meter of reasonable accuracy for measuring volt-ampere hours for circuits on which the range of power. factor variation is known. In carrying my invention into effect I provide a meter having at least two inductiondriving elements which meter is actuated in accordance with the sum of the torques of the" the range of power factor for whichthe meter is designed.

The features of my invention to be novel and patentable ;.will..be pointed out in the claims appended hereto, For a better understanding of my invention reference is made.

in the following descriptionto the accompanying drawing in which Fig. 1 represents a perspective,

View of the essential parts of a single-phase voltampere hour meteras connected to a circuit to be meteredthereby and Figs. 2 and 3 are vector diagrams of the current and. voltage phases of the .two 'drivingj meter elements of Fig. 1 showingwhatloccurs with varying power factor.

It is well known fthatin the induction type of watt-hour meter maximum torque occurs .for given values of voltage and current fluxes when said fluxes are degrees out of phase. Usually the induction watt-hour meter has its voltage electromagnet of such high effective reactance and low resistance that the flux produced thereby lags 90 degrees behind the impressed voltage. A lag coil orplate contributes to this 90 degree relation and serves as ameans of exact adjustnient. The current flux is' in phase with the current so that the j 90 degree relation of current and voltage fl'uxe'sthus exists when the current and voltage of the circuit being metered are in phase or when the power factor of the circuit is unity. r V

One of the induction meter driving elements of my meter may be considered to be of the 'char- The other induction meter driving element of the volt-ampere hour meter is arranged to have; its current and voltage fluxes as near degrees which are believed apart in time phases as'practicable at unity power factor. This may be accomplishedby using a voltage electromagnet of low reactance and connecting considerable resistance-in its energizing winding so as "to "bring its current 1 substantially in phase with its energizing voltage andlikewise substantially in "phase With-the'current in the current' electromagnet of this driving element and then reversing the-connections 'ofthe voltage energizingwi'ndin g;

I When bothof' the; driving elements are connected to' the same power circuit the positive torque of one decreases while the positive torque of the other increases with" a change in lagging power factor-. Then by properly relating their '5 One of these elements Ill is usually adjusted'as a watt-hour meter, e.; its vbltage fiuxla'gs behind-the current fiuxby'90 degrees'when the power factor'ofsth'ecircuit'is' unity. Thesecond dr'iv ing element ll does not havetlie quadrature flux phaserelation'and moreover, in the usual case,

its-voltage coil. is-reversed as compared to the voltage coil ofdriving element Ill so thatits voltage flux-'niaybe consideredto lead the current flux by an'angle'which is'considerably in excess of'90 degrees at unity power'faotorj Then as the power-factorbecomes less than unity and'is lagging the torque.of; thi s second; driving element II will increase while that of the. first element ID will decrease. r The meter, torque isthe .sum of' the "torques of the two fdri vi'ng elementsandfrernains'Substantially proportional to volt-jampres over a considerable power, factor range: 'Ihei'meter shaft is indicated at 13, the register at M and thedamp -f ing magnets partially broken away, at 15; 7

Meter elementlll comprises the voltage electromagnet l6 and current electromagnet I1. Meter element I I has a voltage, electromagnet l8 and current electromagnet I9. The current electrow magnets maybesimilar an d their coils are connect ed in series: with thes econdary of the cur rent transformer 20 having its primarytraversed by the current in the circuit 2 I Thevo1t age electromagnets 'are'not identical. Electromagnet I6 is a standard watt-hour meter potential electromagnet havinga lag plate indicated at 22 and a light load plate indicated at 23. Electromagnet l8 has no lag plate and need not have a light load plate. It has a lower inductance magnetic circuit by reason of increased width of air gap at the points 25 than does electromagnet Hi. The resistance of its coil circuit is increased by means of a non-inductive resistance 26 which is preferably adjustable. The coil circuits of these voltage electromagnets are connected in parallel to the line 2| but the coil of electromagnet I8 is reversed with respect to the coil of electromagnet IS.

The difference between the two driving meter elements so far as operation is concerned may be explained by aid of the vector diagrams of Figs. 2 and 3. In Fig. 2 E represents the voltage flux vector and I the current flux vector of driving element [0 at unity power factor. It is noted that the voltage flux lags the current flux by degrees and under these conditions the torque of element I 0 will be a maximum. In Fig. 3, I represents the current flux of driving element H. It has the same value and phase position as the current flux in element I0. In. 3 the dotted line. arrow e would. represent the voltage flux of element. II had it not been reversed and -e represents the voltage flux as reversed. Considering this voltage flux as before reversal it has a smaller value than E, Fig. 2, for reasons that will appear later. Qwing to the absence of a lag plate, the presence of the non-inductive resistance 26. and the enlarged air gap at 25 the effective inductance of this voltage electro-magnet i8 is insuihcient to lag the fluxthereof 90 degrees. The angle of lag is that corresponding to angle a, which for calculating purposes may be considered 10 degrees when the powerfactorof the circuit is unity. Now when. this flux is reversed to -e it may be considered to lag, the current flux by 180+a. or to lead thecurrent flux by (180-4) degrees when the power factor of the metered circuit 2| is unity. It will be understood that the vectors thus far described are for a given inphase current and voltage of circuit 2|.

Under this conditionthe torque of element In is El and the torque of element H is -e times that component of I which is in quadrature. :eIsin (1:662 in Fig. 3.

In. Fi 2 the current flux leads the voltage flux while in Fig. 3 the voltage flux may be considered to lead the current flux at unity power factor so that the torque represented by E1, in. Fig. 2., and e[ sin a=eQ, Fig. 3, are reversed and the meter torque is then EI- 61 sin a or considering that sin a in this case has'a negative sign the meter torque T=EI+ (-eI sin a) (I) When the line current lags behind the line voltage corresponding to somepower factor cos the torque of meter element 10 reduces to the value EI cos 1p. This is represented in Fig. 2. where the line current has shifted degrees in a lagging direction to the positionindicated by dotted line I1.

In meter element ll this power factor causes the current vector I to shift to. dotted line position I1 also. It is evident that as the current vector shifts from position I to. position I1, in Fig. 3, the negative torque of this meter element first reduces to Zero as the quadrature component Q reduces to zero when. =c and then reverses and increases until the reversed quadrature component becomes Q1. The torque is then eI sin t-a.) =IQ1 in Fig. 3 and the total meter torque becomes This is the general torque equation for all angles of 41 including unity power factor equation (I) because in equation (I) where =o, cos =I and sin (-a) =-sin a.

The voltage flux vector e or e is proportional to E and thus e=E times a constant C.

Thus

Substituting EC for e in this general torque equation (II) Now it can be shown and it will be shown that if the proper value is taken for C the quantity [cos +C sin (a)l remains substantially constant over an appreciable range of power factor or value of 1;! and that therefore over such range of power factor the meter will measure voltamperes or EI within a satisfactory degree of accuracy. Let it be assumed that the power factor of power circuit 2| Fig. l varies between 90 and per cent and we desire to measure the volt-amperes of this circuit by the meter of Fig. 1. Let it be further assumed that the angle a, Fig. 3, of this meter is 10 degrees and that we use-the value .2 for C. Then for differentpower factor 100 and 90 the torque variation may be found from the following table- 1.00 -l0 174 035 .965 5 996 5 087 016 980 o 985 o 000 .000 985 15 966' 5 087 016 .982 20 94 10 l 174 035 975 25 .91 15 260 052 .962

It is seen that there is a variation of only about 2 per cent in the expression cos +C sin (a-) over this range of power factor and hence the meter will measure volt-amperes within such range of accuracy.

The constant C: .2 may be incorporated in the meter by reducing the voltage flux of element II as compared to element l0, by increasing the armature air gap for element II as compared to element I0 or by any other way or combination of ways so as to reduce the torque constant of element H as compared to element ID.

The invention is not limited to the power factor range, angle of a, and constant C used in the above illustration. For example, let us assume we. desire a meter for measuring volt-amperes over a powerfactor range corresponding to variations in 5 from 25 to 35 degrees, that angle a, Fig. 3, is reduced to zero in any suitable way, for example, by including a suitable condenser in the voltage winding of element II and we find that the value to be given C is .5.

When a=0 (a) equals 5 and the general torque equation may be simplified to T1=EI (cos +C sin Then our table for (cos +C sin 1;) for difierent values of between 25 and 35 degrees is as follows:

11 Cos Sin 0 (sin 11 (Cos +G sin 48) It is seen that the error of volt-ampere measurement in the meter of the last illustration is less than 1 per cent over a range of power factor be tween .818 and .90.

Where it is required to cover a range of power factor variation which is too great to be covered with accepted accuracy by one such meter, it will be desirable to use two meters designed to measure volt-amperes over different selected power factor ranges and have the one which is the most accurate at any given instance operate a common register in the manner shown in Fig. 1 and explained in my United States Letters Patent No. 1,530,322, March 17, 1925.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof but I desire to have it understood that the apparatus shown is only 11- lustrative and that the invention may be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A volt-ampere-hour-meter comprising a rotatively mounted armature of conducting material, a pair of induction meter driving elements operating on said armature, said elements having voltage electromagnets connected in parallel but reversed with respect to each other and having current electromagnets connected in series, one of said elements producing a torque on said armature which decreases with a given decrease in 7 power factor and with the other of said elements producing a resultant torque on said armature in the same direction which increases with such a decrease in power factor, the torque constants of said two meter elements being such that the resultant torque of both elements remains substantially proportional to volt-amperes over a considerable range of power factor variation.

2. In combination with a single phase alternating current circuit the power factor of which varies over a given range, a meter for measuring,

the volt-amperes of said circuit comprising a rotatively mounted armature of conducting material, a pair of induction meter elements cooperating with said armature to produce induction meter torques thereon, said elements having voltage electromagnets connected to be energized in proportion to the voltage of said circuit and having current electromagnets connected to be energized in proportion to the current of said circuit, one of said meter elements having its voltage flux lag its current flux by 90 degrees and the other meter element having its voltage flux lag its current flux by approximately 180 degrees when the power factor of said circuit is unity, one meter element producing a torque on said armature in a given direction which decreases with a decrease in the power factor of said circuit and the other meter producing a resultant torque on said armature in the same direction which increases with such decrease in power factor, the torque constants of the two meter elements being so related that over said given range of power factor variation the resultant torque on said armature is substantially proportional to the volt-ameperes of said circuit.

3. An induction volt-ampere-hour-meter comprising an armature of conducting material, a pair of induction meter elements cooperating with said armature to produce torque thereon, said meter elements having voltage electromagnets which are energized in parallel and current electromagnets which are energized in series, the current fluxes of said elements being in phase and the voltage flux of one element lagging its current flux by 90 degrees when the voltage flux of the other element lags its current flux by approximately 180 degrees whereby the torque of one meter element is substantially a maximum when the torque of the other element is substantially a minimum, the torque constants of said meter elements being different and so related that the sum of their torques is substantially proportional to volt-amperes over a selected range of lagging power factor variations.

4. A volt-ampere-hour-meter comprising a rotatively mounted armature of conducting material, a pair of induction meter driving electromagnetic elements operating on said armature, one of said elements being a watt-hour-meter element having voltage and current windings and the other element having voltage and current windings connected so as to be energized in proportion to the voltage and current windings respectively of the watt-hour-meter element, said other element having a voltage electromagnet whose flux is substantially in phase with its energizing voltage and substantially 180 degrees out of phase with the current flux of said element whereby the torque produced thereby is substantially a minimum when the torque of the watt-hour-meter driving element is a maximum and the torques of said elements in a given direction with respect to the armature vary oppositely over a given range of power factor variation, the torque constant of said other meter element being less than that of the watt-hourmeter element by an amount which causes the sum of their torques to be substantially proportional to volt-ampere hours over a selected power factor range.

5. A volt-ampere-hour-meter comprising a pair of induction meter driving elements each having voltage and current electromagnets, a common armature of conducting material on which both driving elements operate to produce torque, connections for energizing the voltage electromagnets in parallel and the current electromagnets in series, one of said driving elements producing a torque proportional to EI cos and the other element producing a torque in the same direction on said armature proportional to E1 sin where E and I are the voltage and current respectively applied to the voltage and current electromagnets and is the phase angle between such current and voltage, the torque constants of said elements differing by a value 0 a such that cos +C sin is substantially a constant over a considerable range of variation of whereby said meter is enabled to measure voltampere hours over such range of variation of 4 with acceptable accuracy.

WILLIAM H. PRA'I'I. 

